Early Critters in Microbial Mats: Evolution or Just a Strange Environment?

For many billions of years, the only life that existed on Earth was microbial, that is, microscopic organisms that we generally call bacteria. These were commonly so abundant that microbial mats basically covered much of the Earth's ocean seafloors.

Then during the Cambrian, a little more than a half billion years ago, animals evolved and burrowed into the microbial mats and took advantage of this rich food source. Of course, that means they eventually ate up the mats.

Many Cambrian animals have a seemingly strange morphology, and have been thought by many to represent early "evolutionary experiments." Among these are the helicoplacoids-the earliest known echinoderms and ancestors of modern animals like the starfish. Shaped like a football, a helicoplacoid had "armor" that was essentially small mineralized plates formed into spirals. Even its food-gatherng organ was a spiral that wound around its body.

David Bottjer, of the University of Southern California, does not agree with the "evolutionary experiment" interpretation of how these animals came about. He will outline a different approach to understanding these strange morphologies on Thursday, November 8, at the Geological Society of America's annual meeting in Boston. "Many early animals were well-adapted, via evolutionary processes, to the unusual (and now usually non-existent) microbial-mat-covered seafloor environments that were typical for the Cambrian. So, rather than the animals being particularly unusual, we are saying that the environments were!" explained Bottjer. "And, being evolutionarily well-adapted to an unusual environment gives an animal a strange morphology, to our modern eyes. So we are suggesting a different evolutionary explanation than what has been offered before, and, in that sense, are breaking from tradition."

This discovery provides a piece for the ongoing puzzle work of understanding how animal life first evolved on Earth.

 Written by Kara LeBeau
GSA Staff Writer

CONTACT INFORMATION

During the GSA Annual Meeting, November 4-8, contact Ann Cairns or Christa Stratton at the GSA Newsroom in the Hynes Convention Center, Boston, Massachusetts, for assistance and to arrange for interviews: (617) 954-3214.